


Temporary Lust, Lasting Sorrow

by pinkheichou



Category: Shingeki no Kyojin | Attack on Titan
Genre: Age Difference, Alpha Eren Yeager, Alpha/Beta/Omega Dynamics, Knotting, M/M, Mating Cycles/In Heat, Omega Armin Arlert, Omega Verse, POV Eren Yeager, Possessive Behavior, Possessive Eren Yeager, Shameless Smut, it's kind of an open ending too tho, lmao who am i kidding the ending is full angst, the ending has light angst
Language: English
Status: Completed
Published: 2017-12-28
Updated: 2017-12-28
Packaged: 2019-02-23 04:08:52
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 2,466
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13182060
Author URL: https://archiveofourown.org/users/pinkheichou/pseuds/pinkheichou
Summary: Armin went into his first heat and Eren wants to help him get through it.He didn't know, though, what that would do to him.





	Temporary Lust, Lasting Sorrow

**Author's Note:**

> We don't have enough Eremin a/b/o fics and we don't have enough Eremin age gap fics...
> 
> So here I am c;

Armin’s breath was erratic—too erratic. So Eren placed a flat hand on the juncture of his chest and throat. “Armin, breath. Please. Don’t forget to breath.”

The blond’s head shifted to the other side, lips bitten hard it almost drew blood. Armin moaned as he gushed out a new wave of pheromones.

Eren took that candid smell in, and it drove him to blissful madness.

He looked down at the lean naked body under him, watched how it transpired a glossy sheen of sweat on the skin, glistening sumptuously.

Eren was kneeling and hovering above him, naked too. His dick was almost fully hard, just from the sight of Armin’s body in heat and the smell he was encased in.

Armin had his legs bent and spread them more now, dug his fingers into the puckered rim of his ass and spread his slick cheeks wider as well. He sobbed, “Eren. Please. Please, please, please. Fuck me. Put your cock inside. Fuck me. Give me your knot. Just,” He swallowed, choked on his breath, and Eren had to remind him to breathe once more, had to keep his head still, eyes locked so that Armin wouldn’t lose himself during his heat. His  _first_  heat. Armin went on with a quivering bottom lip and glassy eyes, “Just anything. Anything is fine. But, please, don’t leave me empty. Eren, please. My fingers aren’t enough. I need… I need something else to fill me. I can’t take it anymore.” At this point, Armin couldn’t present himself more splayed open for Eren than he was already doing so right now.

Surely, Eren’s Alpha side was brought to insanity with that.

Armin was his friend, a good friend. He was helping him out, Eren told himself.

And it was at that very moment that he remembered the previous conversation with his father.

_“Armin is in heat?” Eren stunned, looked at his father with incredulous eyes._

_Grisha faintly nodded. “Yes, he is. And it’s early for him, actually. Too early. Armin is only 14. Male omegas go into heat at the age of 16 _—_ at the earliest. Even then, it is more usual for them to hit that point later in their life.”_

_“Is that bad? I mean… Armin…”_

_“It isn’t bad as per se. But, well, I am not allowed to give him any suppressants because his body is not developed enough to process the substances. For the time being, I gave him harmless herbal sedatives instead. However, it won’t do anything against his heat, it’ll just ease off his bodily functions which have to deal with the effects of a body in high sensitivity and a feverous sexual drive. This is the first day of Armin’s heat and it is most likely a bit too much for him. So…”_

_Eren blinked fast. “You want me to fuck—”_

_“To take care of Armin, yes.” Grisha held a solid look on Eren, lips pressed together as he nodded firmly once. “You and Armin aren’t strangers. You two know each other for long. I’m sure, you, as an Alpha also, would take good care of him.”_

_“But dad, I’m an adult. Is that… Is it okay for me to…”_

_Grisha displayed a small smile. “Don’t worry about that, son. Of course, I’ve talked to Armin before. You’re the only one who he’s trusting. Armin’s parents have been informed as well, and their consent – while it is still all about Armin’s choice – is guaranteed.”_

_Eren’s gaze wandered to the floor, unfocused._

_Grisha tried to encourage him with, “You aren’t that old yet. Early 20 is fine. For Armin, too.”_

_“A-And, and what about birth control?”_

_“He can’t get pregnant. That’s_ impossible. _He shouldn’t have gone into heat in the first place.” Grisha shrugged and adjusted his glasses on the bridge of his nose._

_Eren met Grisha’s eyes again, a stern glance that softened in the end. “Okay. All right, I will do it.”_

_“Good.” The surface of Grisha’s glasses reflected the light as he lowered his head before he raised it again. “One last thing, though. I hope you know that I don’t want to force you to do it.”_

_A little pause where they maintained their mute glances until Eren was the one to smile genuinely. “I know. I’m doing this because I want to help Armin. If I can prevent him from being in tight and needy discomfort, then I will do it.”_

So here he was, being a witness of Armin’s first heat and also taking care of it as an Alpha.

Armin mewled, “Eren, please.” Tears began to roll down.

“It’s all right. No need to be desperate anymore. I’m here, okay? I’m here for you.” Eren lifted one of Armin’s legs to his shoulder and held it there, his other hand guiding his cock to Armin’s leaking entrance. That Armin had released a good amount of slick made it only clear how pent-up he was.

Eren rasped out his first moan when his tip pinched inside, engulfed by tightness and  _hotness_. An amazing feeling that scraped against his restraints. “Oh my god, Armin. Your ass is sucking me in.”

“Eren, Eren, Eren…” Armin sang in a mantra, and Eren thrust fully into him now.

When Armin looked down on himself and saw how Eren’s gorgeous Alpha cock was wholly seated inside of him, he revelled in that new  – never known before  – feeling; his hands pressing on Eren’s lower abdomen. Streams of tears stained his face as he sobbed Eren’s name over and over again.

Eren cupped one of his wet cheeks, inched his face closer to the other’s, started to rock into Armin at a steady pace. His cock was enwrapped by Armin’s ass as much as was possible, was clenched between slick and pliant walls.

The prickling sweet Omega scent intermingled with Eren’s musky Alpha odor, which oozed out of his pores more prominently because of the presence of an Omega’s heat. Eren lost himself in it just as Armin was lost in the thrills of his heat.

Eren picked up his pace, keen to fuck Armin raw with how beseeching Armin was, praising Eren for having such a great,  _thick and throbbing_  cock. It awoke his feral Alpha instincts and Eren let them take over him.

Right now, Armin looked the prettiest to him. The way he writhed and wound under Eren’s touches and thrusts fuled Eren with pride he drank in greedily. It squeezed out a bestial growl from his throat, sounding scathingly sharp.

Yeah, Eren wanted to black everything out and give in to the pleasure of an Alpha mating with an Omega in heat.

He had to forget, especially after countless attempts of forgetting his dad’s last words which he had stubbornly rejected to retort to.

_“Eren,” Grisha put each of his hands on Eren’s upper arms. His voice was serious but fond. “I’ve been noticing how your scent would change whenever Armin was around you.”_

_Eren had gone into a momentary freeze, blood going stiff and heart clenching. Looking into his father’s eyes as if he was caught out committing a crime, Eren’s mind started to spin, the words whirling in his ears, giving him a headache. The physical ache, though, could not conceal his true emotional feelings._

_And yet, stubbornly, Eren slapped his dad’s arms away with a brisk move. “There is no meaning behind that.” had been all he had monotonously said to Grisha._

_Their talk had ended right there and then, Eren heading for the room Armin had been stationed in._

The denial… would come back.

It showed itself again; right now, to be specific.

The worst of the worst times for Eren.

Thoughts of  _‘Armin, you are so amazing, so gorgeous, so precious.’_  and  _‘Your body matches perfectly with mine.’_  and  _‘You smell so great. You have the most beautiful fragrance ever.’_  abused Eren’s mind ruthlessly, not letting him any room for denial or reluctance.

Eren –  _his Alpha –_  longed for the one it desired.

When Eren was already fucking hard into Armin, coaxing out shameless and vocal moans out of the other, he picked him up, thrust into him while Armin was sat on his lap until he would start fucking himself on his cock.

Heat and sweat blazing under his skin, Eren was clouded by the sensation of having an Omega –  _Armin –_  by his side. Armin wasn’t his first Omega. But surely this felt more special than all the other times he had had sex with an Omega.

Eren couldn’t hold back anymore.

The craving flooded him.

Armin cried out lewdly on his shoulder. “Ah, E-Eren… your—”

Eren’s pointer finger rubbed over Armin’s scent gland on his neck, causing for Armin to startle at first and scream moans to it. “Shhh, it’s fine, Armin, it’s fine.”

Armin grabbed the back of his shoulders hard, pulled his nails down his skin. “Your scent, Eren… so good. Your dick… ‘s so good. Everything feels  _so good_.”

Eren groaned senselessly.

A single word.

_Mi—_

_No,_  he thought. Couldn’t happen. Couldn’t be,  _never could._

Croons vibrated in the inner of his throat as he brushed Armin’s hair away from his neck while Armin would bounce adamantly on his cock, ass wet and cock dribbling ounces of pre-come. Eren set his lips next to Armin’s scent gland and had to use all of his self-control in order to not mar his skin open with his teeth.

He sucked on the skin instead, sucked hard, tongued the parts that were circled by his mouth.

 _For now, you are_  mine,  _Armin._

There was it.

“Fuck…” Eren let go of him, gripped Armin’s hips and gyrated his own ones aggressively, pounding into Armin with fervor. He didn’t lose eye contact with the other, stretched his own throat, tipped his head back a bit so that he wouldn’t miss a single reaction mirrored on Armin’s face.

Brows creased from eagerness, lips mauled by teeth, eyes dilated, and Eren freed his yearning from its cage.

_You’re here with me now, Armin. You’re mine right now. Mine, mine, mine._

_But I want you to be mine forever!_

Eren closed his eyes as these particular thoughts, his innermost desire, ate him out from the inside.

By now, his previous statement of only wanting to help Armin sounded grotesque to him.

Eren felt pathetic. He  _was_  pathetic, so he thought.

He could never… Armin…

“Eren…” Armin brought a part of Eren back to reality, the other part wallowed in bittersweet void still, “Your knot, please. Eren, I—”

“I’m almost, hngh, there. Almost there, Armin.” Eren grunted hot breath into the crook of Armin’s neck. His nose nuzzled Armin’s scent gland again. His neck looked so pretty. So smooth. So empty without a mark.

And it was then that the idea of wanting to bite into Armin’s neck, to claim it and scratch other parts open as well, to itch his possession into Armin’s body with teeth and nails, sounded so great. So perfect. He would lick and suck on every bloody spot. And he would kiss every mark pretty.

The mating mark that would form on Armin’s neck would become something holy to Eren. And Eren would kiss every part that was Armin, all the while whispering how Armin was his.  _Mine, mine, mine._

_Please be mine._

Eren emptied his shot inside Armin, blessing him with the feeling of getting filled up before the base of Eren’s cock started to swell, gradually locking Armin’s body with his. During that process, Armin would come as well, shouting into the night, eyes rolling back as his first orgasm ever and his first heat ever overwhelmed him in form of the feeling of utter lust.

The sight of Armin ascending to an ecstatic state – ascending to ecstasy  _because of him_  – was a pure blessing to Eren. He kissed Armin’s chest once, lips coming into touch with sweat that was rich in an Omega’s heat and scent, as he cautiously lowered Armin to the bed while the knot lasted for a little while longer.

They lay like that on the bed, facing each other. Armin was mainly trying to catch his breath while Eren would finger the crack of Armin’s ass, though not taking his eyes off of the other.

Armin was too wrung out to think properly. “Eren?”

“Yeah?” Eren breathed hoarsely.

“Eren, I— hahhh,” Eren’s knot deflated and with that, his spurt leaked from Armin’s ass, giving Armin a giddy feeling. But it still felt good in some way. “Eren…”

“It’s okay,” Eren tugged a few strands behind Armin’s ear, endearingly, “You don’t have to talk or think right now. Have a rest.”

“Hmhm.” Armin hummed, eyes already shut as he pulled his knees up and snuggled into Eren’s side, cuddling his arm. While Armin was, technically speaking, still in heat, the current moment kind of counted more as an “aftermath” of it. But of course, especially now, Armin’s first instincts would tell him to stay close to an Alpha—the one you spent your heat with.

Eren’s face nuzzled into Armin’s hair, wanted to be selfish for this one second, and so he breathed in Armin’s scent. It smelled so good. Armin smelled so good, it took Eren’s breath away.

At the same time it ached him so much—so, so, so much. The pain numbed him to the point that he didn’t sense when it was that Grisha had entered the room.

“Eren.” he called out calmly.

Eren turned around, slowly, feeling as if his soul was ripping itself out of his body, his primal instincts a howling chaos. By the time he looked up to his father, his sight had already gone blurry, a flow of tears pouring down his face, stealthily.

Grisha would like to be spared from the sight of his own son crying in pain, but at the same time he understood. He knew.

 _What else could be a reason for an Alpha’s altered scent when being around an Omega other than the Omega being dear and significant to them?_ , Grisha sighed lowly. Deep down, he wished for his son to come to terms with himself. To not fight with his irrational, self-loathing side anymore.

To accept and appreciate what he actually deserved.

But Eren was far from that.

“Dad…” he croaked, every intake of breath stung in his chest.

Eren shouldn’t have agreed to this. He shouldn’t have done this in the first place. He was at own fault for having inflicted pain on himself.

What else could hurt an Alpha more than the scent and presence of an Omega he wanted but couldn’t have; couldn’t claim for himself.

Eren wanted Armin.

_Mine._

Ever since he first laid eyes on him.

Ever since then…

_Mine, mine, mine. Please._

Ever since then, Eren had been infatuated.

**Author's Note:**

> There are a few things in this fic that are open to interpretation ;)))
> 
> tumblr: [pinkheichou](http://www.pinkheichou.tumblr.com)


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